Call `OleInitialize` to fix `DirectWrite` in `TestPlatform` on windows (#12289)

Running the tests on windows currently fails for every gpui test using
the `TestPlatform` with

```rs
called `Result::unwrap()` on an `Err` value: CoInitialize has not been called. (0x800401F0)
```
trying to call `CoCreateInstance`in the `DirectWriteComponent`.

The `WindowsPlatform` calls
[`OleInitialize`](https://learn.microsoft.com/de-de/windows/win32/api/ole2/nf-ole2-oleinitialize)
which internally calls `CoInitializeEx` so I just copied that to the
`TestPlatform`.

Release Notes:

- N/A